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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 6  |  Issue : 3  |  Page : 287-293

The effect of inspired oxygen concentration on postoperative pulmonary atelectasis in obese patients undergoing laparoscopic cholecystectomy: a randomized-controlled double-blind study


1 Department of Anesthesia, ICU and Pain Therapy, Faculty of Medicine, Menoufia University, Shibin El-Kom, Menoufia Governorate, Egypt
2 Department of Anesthesia, ICU and Pain Therapy, Central Aga Hospital, Ministry of Health, Dakahlia, Egypt

Date of Submission17-May-2018
Date of Acceptance26-Feb-2019
Date of Web Publication29-Aug-2019

Correspondence Address:
MD Ashraf M Eskandr
3 Yassin Abdelghafar st., Shibin Elkoom, 32511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/roaic.roaic_40_18

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  Abstract 

Introduction Atelectasis is the most important postoperative pulmonary complication in obese patients following general anaesthesia. The study aimed to determine the effect of inspired high versus low oxygen concentration on pulmonary atelectasis in obese patients undergoing laparoscopic cholecystectomy.
Patients and methods A total of 60 patients, American Society of Anesthesiologists I–II, of both sexes, aged 20–60 years, BMI more than 30 kg/m2 and scheduled for elective laparoscopic cholecystectomy were randomly assigned to group I inspired 40% oxygen and group II inspired 90% oxygen after endotracheal intubation and for 2 h postoperatively. The effect of inspired oxygen concentration on atelectasis approved by computed tomographic scan and radiography was determined 24 h after surgery. Oxygen saturation, the partial pressure of arterial oxygen and carbon dioxide, tension, pulmonary functions and haemodynamic parameters were also recorded.
Results Atelectasis was detected by computed tomography scans of the chest performed in the first postoperative day in 60% of patients in group I, whereas it was detected in 76.7% of patients in group II without significant difference between the groups, and it was determined in 33% of patients in group I compared with 46% of patients in group II, without significant difference between the two groups by radiographic examination. Postoperative forced vital capacity and forced expiratory volume in 1 s were significantly reduced in the two groups compared with the preoperative values in both groups without significant difference between the two groups. The intraoperative partial pressure of arterial oxygen values showed an insignificant change in the postoperative measurements between the groups.
Conclusion Administration of low percentage of oxygen concentration (40%) was associated with decreased incidence of atelectasis without worsening of pulmonary function.

Keywords: atelectasis, laparoscopic cholecystectomy, obese, oxygen concentration


How to cite this article:
Eskandr AM, Atallah HA, Sadik SA, Mohamemd MS. The effect of inspired oxygen concentration on postoperative pulmonary atelectasis in obese patients undergoing laparoscopic cholecystectomy: a randomized-controlled double-blind study. Res Opin Anesth Intensive Care 2019;6:287-93

How to cite this URL:
Eskandr AM, Atallah HA, Sadik SA, Mohamemd MS. The effect of inspired oxygen concentration on postoperative pulmonary atelectasis in obese patients undergoing laparoscopic cholecystectomy: a randomized-controlled double-blind study. Res Opin Anesth Intensive Care [serial online] 2019 [cited 2019 Oct 19];6:287-93. Available from: http://www.roaic.eg.net/text.asp?2019/6/3/287/265717


  Introduction Top


Postoperative pulmonary complications are a major cause of morbidity, mortality and prolonged hospital stay and increased the cost of care after surgery [1]. Atelectasis is a serious complication and one of the most dangerous postoperative pulmonary complications [2]. Pulmonary atelectasis occurs in 85–90% of healthy adults within minutes after the induction of general anaesthesia, and up to 15% of the entire lung may be atelectatic, in the basal regions, resulting in a true pulmonary shunt of 5–10% of cardiac output [3].

Obesity reduces respiratory functions, affects all parameters of lung function testing and is the main cause of postoperative pulmonary complications after general anaesthesia. Obese patients have lower lung compliance, chest wall compliance and total respiratory compliance [4].

Atelectasis is more marked in obese patients because of lower resting lung volumes, smaller airway calibre and cephalad displacement of the diaphragm in the supine position [5]. The main mechanisms underlying the atelectasis formation in obese patients are compression, loss of surfactant or impaired surfactant function and absorption of gas (oxygen) from alveoli behind closed or intermittently closed airways [6].

Ventilation for only a few minutes with 100% oxygen causes a significant increase in atelectasis after anaesthesia induction compared with ventilation with lower oxygen concentration [7]. Moreover, high inspired oxygen concentration, even for brief periods of time, has been shown to induce atelectasis. The inspired oxygen fraction (FiO2) used during general anaesthesia will influence atelectasis formation. Atelectasis will not happen during general anaesthesia if the inspired oxygen concentration is 30% or less. However, this is not recommended, because decreasing the inspired oxygen concentration will also decrease the duration of nonhypoxic apnoea [8].

However, no clear association between atelectasis formation and oxygen concentration during maintenance of anaesthesia has yet been established, and several other harms and benefits still need further investigation [9].

This study was designed to compare the effect of high inspired 90% FiO2 and low inspired 40% FiO2 on postoperative pulmonary atelectasis in obese patients during laparoscopic cholecystectomy.


  Patients and methods Top


The study was carried out after approval of the Local Ethics and Research Committee of Anaesthesia Department, Faculty of Medicine, Menoufia University Hospitals, Menoufia, Egypt, on 18 June 2017. The study was also registered at the Pan African Clinical Trial Registry (PACTR201802003138123) (http://www.pactr.orghttp://www.pactr.org). This prospective randomized-controlled trial (double-blinded) was carried out on 60 patients, American Society of Anesthesiologists I–II, of both sexes, aged 20–60 years, having a BMI more than 30 kg/m2 and scheduled for elective laparoscopic cholecystectomy among those presenting to Menoufia University Hospital from July 2017 to February 2018. Exclusion criteria included patient refusal to be included in the study, history of current symptoms of acute or chronic pulmonary disease, history of current symptoms of cardiac disease, fever or infection and patients who needed open cholecystectomy because of a surgical cause.

Before the surgery, all patients had a preoperative visit for clinical examination, preoperative laboratory investigation revision and patient consenting.

On arrival of the patient to the preoperative holding area, a wide bore intravenous catheter was inserted, and Ringer’s lactate solution was started; a five-lead ECG with ST-segment analysis was placed for continuous ECG monitoring. Noninvasive blood pressure, oxygen saturation (SpO2) and end-tidal CO2 were also monitored.

All patients were premedicated with midazolam 2.5 mg and 50 μl fentanyl. A radial artery catheterization was performed under local anaesthesia for arterial blood gas (ABG) sampling after performing Allen’s test.

General anaesthesia was induced with a FiO2 100% with fentanyl (1–2 μg/kg), propofol (2 mg/kg), and cis-atracurium (0.15 mg/kg) for endotracheal intubation. After tracheal intubation, patients were divided randomly by closed, opaque envelopes into two equal parallel groups, 30 patients in each group. The sealed, opaque envelopes were opened by anaesthesia nurses. Neither the patients nor the assessors knew the concentration of the inspired oxygen. Group I inspired 40% oxygen and group II inspired 90% oxygen. The lungs were ventilated with a tidal volume of 10 ml/kg, and the volume controlled with zero positive end-expiratory pressure. Anaesthesia was maintained with isoflurane (1.2 minimum alveolar concentration) in the carrier gas. The respiratory rate was adjusted to maintain an end-tidal carbon dioxide partial pressure 30–35 mmHg with an inspiratory/expiratory ratio of 1 : 2. All operations were performed in the morning after an overnight fast. All patients had a nasogastric tube, and a urinary catheter was inserted; these were removed immediately after surgery. Pneumoperitoneum was established with carbon dioxide insufflation, and the intra-abdominal pressure was maintained at 14 mmHg. At the end of surgery, any residual effect of muscle relaxant was reversed by 50 μg/kg neostigmine and 20 μg/kg atropine. After endotracheal extubation, patients were transferred to the postanaesthesia care unit where they received the predetermined oxygen for the first 2 h after recovery, through a nonrebreathing mask system. Subsequently, all patients breathed room air. If any patient suffered hypoxia (SpO2<92% by pulse oximeter), supplemental oxygen was given to him in either group as necessary to maintain oxygenation and he was excluded from the study.

Measurements

  1. Heart rate (HR), mean arterial blood pressure (MAP) and SpO2 were measured and recorded before induction of anaesthesia, every 15 min during anaesthesia and after recovery.
  2. Pulmonary function tests including the forced vital capacity (FVC) and the forced expiratory volume in the first second (FEV1) were measured before the operation as baseline measurements and on the first postoperative day. Measurement of pulmonary function was performed using the spirometer (VIASYS Healthcare Microlab, Warwickshire, UK), whereas the patients were in sitting position.
  3. An ABG measurement was obtained after insufflation and after 2 h of recovery at the randomly assigned fraction of inspired oxygen.
  4. Chest radiography (posteroanterior and lateral views) were performed before operations with the routine preoperative investigations and on the first postoperative day with the patients in a semisitting position. Chest radiographs were evaluated for atelectasis with Joyce and Baker [10] modification of Wilcox severity scoring: 0=no atelectasis, 1=plate atelectasis, 2=segmental atelectasis, 3=partial lobar atelectasis, 4=complete lobar atelectasis and 5=complete lobar atelectasis in addition to any of the above.
  5. The primary outcome was computed tomography (CT) scans of the chest obtained on the first postoperative day, ∼24 h after surgery. CT scans were evaluated for atelectasis by defining lung density in terms of Hounsfield units [11]. Lung densities between −100 to +100 Hounsfield units are considered as nonaerated (atelectasis), densities between −500 to −100 as poorly aerated areas and densities between −500 to −1000 as normally aerated areas [11],[12].


All postoperative measurements were performed before receiving the first chest physical therapy.

Sample size calculation

When designing the study, we assumed the differences in atelectasis between the studied groups and the SD of 20% each. Setting α to 0.05 and β to 5%, we calculated that an appropriate group size would require 23 patients. We planned to include 30 patients per group (N=60) to allow for potential dropouts or protocol violations.

Statistical analysis

Data were analysed with SPSS, version 21 (SPSS Inc, Chicago, Illinois, USA). The normality of data was first tested with the one-sample Kolmogorov–Smirnov test. Qualitative data were described using number and percentage. Association between categorical variables was tested using χ2-test. Continuous variables were presented as mean±SD. The two groups were compared with Student’s t-test, whereas paired groups were compared by paired t-test. P-value will be considered to be of statistical significance if it is less than 0.05.


  Results Top


From the 78 patients who were eligible for the study, six patients were initially excluded, and two patients refused to participate. Of the 70 patients allocated to the study groups, 10 patients (three in group I and seven in group II) were excluded from further analysis, because they needed supplemental oxygen more than 2 h postoperatively to maintain adequate oxygenation (SpO2>92). Data from the remaining 60 patients (30 patients in each group) were analysed ([Figure 1]). Demographic characteristics of the 60 patients and the duration of surgery in each group were comparable ([Table 1]).
Figure 1 Study flow chart.

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Table 1 Comparison between studied groups with regard to demographic data and duration of surgery

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Haemodynamic responses (HR, MAP) of the patients showed no significant difference between them in the two groups ([Table 2] and [Table 3]).
Table 2 Comparison between studied groups with regard to heart rate

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Table 3 Comparison between studied groups with regard to mean arterial blood pressure

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SpO2, as detected by pulse oximeter, was approximately similar in the two groups without significant difference between them ([Table 4]).
Table 4 Comparison between studied groups with regard to oxygen saturation

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In relation to pulmonary function tests, postoperative FVC was significantly reduced in the two groups compared with the preoperative values (P=0.01, 0.001) in groups I and II, respectively; also, postoperative FEV1 was significantly reduced in the two groups compared with the preoperative values (P=0.048 and 0.001) in groups I and II, respectively, whereas the postoperative values showed no statistically significant difference between the two groups with regard to FVC and FEV1 (P=0.11 and 0.08, respectively) ([Table 5]).
Table 5 Comparison between studied groups with regard to pulmonary functions

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In relation to ABG, the intraoperative measurement of arterial oxygen partial pressure showed a significant increase in group II (90% oxygen) compared with group I (40% oxygen) (P=0.001), without significant change in the postoperative measurement between the groups (P=0.18) ([Table 6]).
Table 6 Comparison between studied groups with regard to arterial blood gas

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None of the preoperative chest radiographs showed any detectable amount of atelectasis, but atelectasis was determined in 33% (10 of 30) of patients in the 40% oxygen group I compared with the 46% (14 of 30) of patients in the 90% oxygen group II in the first postoperative day without significant difference between the two groups (P=0.796) ([Table 7]).
Table 7 Comparison between studied groups with regard to radiography and computed tomography atelectasis incidence

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Atelectasis was detected by CT scans of the chest performed in the first postoperative day in 60% (18 of 30) of patients in the 40% oxygen group I, whereas atelectasis was detected in 76.7% (23 of 30) of patients in the 90% oxygen group II without significant difference between the groups (P=0.165) ([Table 7]).


  Discussion Top


The present randomized double-blind controlled study comparing postoperative pulmonary atelectasis in obese patients who received high oxygen 90% or low oxygen 40% concentration during laparoscopic cholecystectomy and for 2 h postoperatively showed that there was a lower incidence of atelectasis in patients who received 40% oxygen without a significant difference between the two studied groups, with insignificant effects on ABG, pulmonary functions and haemodynamics of both groups.

This study results found no significant change in HR and MAP between patients in each group, with the lowest values being at the time of insufflation. This is in agreement with Larsen et al. [13] who studied the effect of pneumoperitoneum on cardiac functions and haemodynamics during laparoscopic cholecystectomy. As changes in ABP and HR are due to the effect of pneumoperitoneum and positional changes during the procedure, these factors are all constant in our study, as all patients undergo the same surgical procedure; hence, no change in these hemodynamics occurs between patients in the two groups.

Moreover, there was no significant change in SpO2 between patients in each group at any time, which was in agreement with Hovaguimian et al. [14] who reported that there was no significant decrease in postoperative SpO2 values in patients exposed to high or low FiO2. In contrast with our results, Zoremba et al. [8] found that the high oxygen group showed a greater decrease in postoperative oxygenation than the low oxygen group, and this may be due to the use of 100% oxygen throughout anaesthesia in his study.

There was an observed significant decrease in postoperative FVC and FEV1 compared with preoperative values, but there was no difference between the two groups at either time; this may have been caused by impaired respiratory mechanisms, obesity and atelectasis formation promoted by general anaesthesia in a supine position. The decrease in FVC and FEV1 followed the same pattern, and FEV1/FVC ratio did not change, suggesting a restrictive pattern in the immediate postoperative period. These results were in agreement with multiple earlier studies [15],[16],[17],[18].

Concerning the intraoperative arterial oxygen partial pressure, it was significantly higher in group II, and this was expected as the result of high inspired oxygen concentration, but there was no significant difference between the two groups in the postoperative values; this was in agreement with a study that was carried out by Akca et al. [19].

The incidence of atelectasis was more in group II than in group I, as approved by radiography and CT findings without significant difference between the two groups. These findings were the same as found by multiple earlier studies comparing the perioperative use of low and high oxygen concentration during general anaesthesia. Likewise, Benoît et al. [20] found that the use of 100% oxygen at the end of general anaesthesia promotes postoperative atelectasis regardless of whether vital capacity manoeuvre (inflation of the lung with 40 cmH2O for 15 s) was performed. In contrast, a vital capacity manoeuvre followed by 40% oxygen prevents postoperative atelectasis formation. Moreover, Rothen et al. [21] reported that the use of 30% oxygen was effective in preventing atelectasis formation during anaesthesia induction. However, this is not recommended clinically during induction of anaesthesia, because decreasing the inspired oxygen concentration will also decrease the duration of nonhypoxic apnoea [8]. Actually, the aim of oxygen inspiration during induction of anaesthesia is to increase the margin of safety before apnoea, which will not occur with the use of only 30% of oxygen inspiration.

In contrast, some studies used 100% oxygen during anaesthesia, leading to increased incidence of atelectasis, and, to prevent this, they have used recruitment manoeuvres. Rusca et al. [22] and Coussa et al. [23] reported that despite the use of 100% oxygen, application of positive end-expiratory pressure throughout the induction period effectively prevents atelectasis formation and improves oxygenation during induction of general anaesthesia in adults and in morbidly obese patients, respectively. Edmark et al. [7] studied oxygen concentration and characteristics of progressive atelectasis formation during anaesthesia, and they found that there were benefits of using 80% instead of 100% oxygen for preoxygenation, and that atelectasis development was faster when the inspired oxygen concentration was higher.


  Conclusion Top


In this study, lung volumes, the incidence of atelectasis and alveolar gas exchange were compared in patients given 40% oxygen or 90% oxygen during laparoscopic cholecystectomy, and the conclusion was drawn that administration of low per cent oxygen concentration (40%) was associated with decreased incidence of atelectasis with insignificant effects on pulmonary function, ABG and haemodynamics. We recommend its use in the type of obese patients selected. Further large and multiple studies in a large number of obese patients with other types of abdominal surgeries have been recommended for approving the safe use of low oxygen concentration in obese patients undergoing different abdominal surgeries.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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